1. Field of the Invention
This invention relates to a tracking control circuit and method for controlling tracking in a digital image recording and reproducing device. Specifically, this invention is a circuit and method for controlling the tracking operation, using a bit error rate which is signified by the number of errors flags set (each flag being set by correcting a detected error) during detection of a sync block. This application for a tracking control circuit and method is based on Korean Patent Application No. 24446/1996 which is incorporated by reference herein for all purposes.
2. Description of the Related Art
Conventional digital image recording and reproducing devices convert analog image signals into digital image signals, and then compress them for recording. The conventional devices also expand the compressed digital image data upon reproduction, and reconstitute the analog signal for output. Such a conventional digital image recording and reproducing device contains a coder and decoder which uses an error correction code (ECC) to prevent a degradation of picture quality during the recording and reproducing processes.
As is well known in this field, the ECC decoder corrects error bits of code data during the reproducing process, using parity bits of a sync block. Occurrence of an error in a sync block is signaled with an error flag. Thus a bit error rate (BER) may be obtained by counting error flags.
FIG. 1 illustrates a configuration of the data-sync blocks of a video sector according to a super density (SD) digital image recording format. As shown in FIG. 1, the size of each sync block is 90 bytes. Each sync block is composed of a sync area (2 bytes), an identification area (3 bytes), a 77 byte data area, and an inner parity area (8 bytes). Each video sector (or data frame) has one hundred thirty eight sequential sync blocks. An outer parity area, where an outer parity is recorded, occupies the remaining data area of the video sector. Data errors in the sync block are corrected by the ECC decoder through inspections involving parity bits in the inner parity area. When a data (or bit) error occurs, an error flag is triggered by the ECC decoder.
To accurately pick up and reproduce information which has been recorded on a medium such as magnetic tape, for example, in the form of the video sector of FIG. 1, it is essential to control the tracking of recorded tracks. The capstan motor should be controlled so that the head can accurately scan tracks containing recorded information. When tracking is not controlled accurately, the sync signals of the sync block (reproduced from the sync area) are not accurately detected during the ECC operation, resulting in frequent errors. Moreover, a burst error can occur.
The following is a description of a conventional tracking control method used in a digital image recording and reproducing device. During recording, an extra bit is added to the 24 bit data block for automatic track finding (ATF). Twenty-five bits of data are recorded on the medium as an interleave non-return-to-zero-inverted recording. The extra bit is added to the 24 bits of data to generate frequencies f0, f1, and f2 which discriminate three kinds of recording tracks from each other. When reproducing data, pilot frequencies f0, f1, and f2 for ATF are detected by an ATF circuit as signals output from a reproducing amplifier. The ATF circuit then controls the tape speed by controlling a servo, using the detected pilot frequencies.
Since the tracking was conventionally controlled through detection of analog pilot frequencies recorded on the tracks, accurate control could not be established. The conventional tracking method has the problem of low recording efficiency because an extra bit for tracking control (to record the distinct pilot frequencies) is added to the 24 bits of data. As a further disadvantage of the conventional ATF system, an ATF circuit for detecting pilot signals of the present, preceding, and succeeding tracks must be independently added to the system, and as a result the circuit of the system is made more complex.